High-voltage electron device



1,62 693 May 1927 H. c. RENTSCHLER men VOLTAGE ELECTRON vnvics Filed Nov. 29. 1922 INVENTOR H141? VEY C PENTSCHL ER ATTORNEY ary electrons emitted from the target.

Patented May 3, 1927.

UNITED STAT-Es PATENT "OFFICE.

HARVEY cnAYToN garm nt, or EAs'r ORANGE, NEW J s Y, ASSIGNOR T0 WESTINGHOUSE LAMP COMPANY, ACORPOR'ATIONOF PENNSYLVANIA.

HIGH-VOLTAGE ELECTRON DEVICE.

Application fi1edNovember 29, 1922. Seria1 N0s603,912.

This invention relates to high-potential electron devices, forexample, X-ray tubes.

vision is made for the dissipation of {electrical charges which develop on the surfaces ofthe glass during operation, wher by puncture thereof is avoided when high voltage is used.

Another object 0t my invention is to so construct X- ay tubes, or other-devices including electron-emitting cathodes, that electron charges developing on the interior of the envelopes thereof, are permitted to leak through to the exterior, thereby obviating "puncture of the walls thereof by reason of the building up of electrostatic stresses.

A further object of my invention is the provision of envelopes for electron devices of such character that punctures are avoided when high voltage is impressed thereon.

Other objects and advantages will beapparent from the following description.

It is well known that the envelopes of electron devices, such as X ray tubes, are subject to puncture when used on high potential. Puncturesof this character usually occur in the "cathode or negative end of the tube. It is thought that this phenom enon is explained by assuming that the insidesurface of the envelope becomes charged by an accuinulation of electrons coming directly from the cathode or reflected from the'anode or target of the device or second- The electrodes exert an influence on the accumulationot the charge, causing a more intense charge to develop in the cathode end of the tube or other envelope.

Such an electron. or negative charge on the inside of the tube will cause the outside surface thereof to acquire a positive charge by electrostatic induction, especially as the surrounding air is ionized by X-rays during the operation of: the device. Such charges tend to accumulate on the opposite surfaces of the glass. causing a tendency to puncture. especially if very high voltage is impressed on the device. Such explanation applies particularly tothe simple case of a high-vacuum, high-voltage X-ray tube with a hot 'cathode and operated from a source of direct current. A tube operated on alternating current will withstand a higher crest voltage than it will when operated on direct current, because time interare allowed between pulses, during which more or less lcakageoccurs, whereby electricalstress is relieved. According to my invention, I prevent undue electrical stress in the envelopes for higlrvoltage electrondevices by providing conductive means for preventing the -accumulation of charges of opposite polarity on the inner and outer surfaces respectivelyof the envelopes there for. Such means may take a variety of forms, for example, gl a. s having greater conductivity may be' employed for thOSGDOl" {tions of the tube subject to the greater electrical stresses or series of conducting plugs or the like may be inserted in those portions of the envelopes subjectyto puncture.

A further modification may comprise coating the exterior and interior surfaces of the envelope in the vicinity of the oathode, that is, in that part of the envelope where puncture is more apt to occur, with a conductive film or coating, and connecting said innerand outer films electrically either by a leading-in conductor through the glass directly between said films or by connecting both films to the cathode.

My invention will be better understood by referring to the accompanying drawing in which, v

Figure 1 represents, diagrammatically, a high voltage X -r'ay tube, shown partly in section and constructed according to my invention; and v Figures 2 and 3 represent similar views of tubes constructed according to slight modific'ations of my "inventive idea.

The evacuated tube 4- (Figure 1.) may be formed of glass or other transparent insulating material and, as shown, may comprise a main substantially spherical compartment and oppositely extending substantially cy lindrical portions 6 and. 7. An electronemitting cathode 8 is preferably sealed into one extension 6 and a target or anode 9 may be sealed into the other extension 7, thereby connecting said films.

3 Lee the glass is allowed to leal; away by means of said conductive members thereby preventing puncture of the glass in the vicinity thereof.

A slight modification of the device shown in Figure 1 may be provided by electrically connecting conducting members 11 on the interior and exterior surfaces of said envelope. Such electrical connection may be made in various ways as by applying to said exterior and interior surfaces, metallic or conductive films 12 and 13, for example, aluminum enamel, or coating said surfaces with metallic foil, for example, tin foil. If the series of conductive members 11 are dispensed with, said coi'iducting films 12 and 13 may be connected in any one of several Ways, for example, as shown in Figure 2, a single wire 14 may be sealed through the glass adjacent said conducting films and directly connected thereto or any desired number of said wires or plugs may be provided The conductive films on the glass reduces the effective length of the tube as an insulator, making it necessary to use a longer tube for a given applied voltage. Instead of providing an ad ditional conductor through the glass, both interior and exterior films may be connected to the cathode 8 of the X-ray tube.

The device represented in Figure 3. is a slight modification of that shown in the preceding figures and may comprise an envelope 15 containing a cathode 16 and an anode or target 17. The envelope 15 is preferably provided with a main substantially spherical compartment 18 composed of glass or other transparent material made more conducting, in any desired manner, than that composing the substantially cylindrical extensions 19 and 91, for example, by incorporating conductive material in the batch of glass used. Large differences in potential between the inner and outer sur faces of the material composing the envelope are thereby prevented from developing and punctures thereto are avoided.

Although I have disclosed what are now considered preferred embodiments of my invention, it is to be understood that the same may be embodied in other electron devices besides X-ray tubes and the embodiments shown are merely illustrative, as my invention is only limited by the spirit and scope of the appended claims.

What is claimed is:

1. An electron device for high potential comprising an evacuated sealed insulating envelope, an electron-emitting cathode and an anode therein, that portion of said envelope adjacent said electron'emitting cathode including material of greater conductivity than the remaining portions of said envelope whereby severe dielectric stresses therein are obviated.

2. An insulating envelope for an X-ray tube or the like comprising a main sub stantially spherical compartment and oppositely directed substantially cylindrical extensions therefrom, the insulating walls of said main compartment being constituted to have a greater conductivity than the material of which the extensions are constructed.

3. An electron device adapted for high potential comprising an evacuated sealed insulating envelope, comprising a main relatively-large compartment and a pair of relatively-small auxiliary compartments extending therefrom, one of said auxiliary compartments supporting an electron-emitting cathode and the other supporting a cooperating anode or target and that portion of the envelope formed as the main relativcly-large compartment being constructed of material of greater conductivity than the remaining portions thereof, whereby severe dielectric stresses therein are oh viated.

4. An insulating envelope for an X-ray tube or the like comprising a main substantially spherical compartment and opp0- sitely directed substantially cylindrical extensions therefrom, the walls of said main compartment to approximately where the extensions are joined thereto being formed of material of greater conductivity than that constituting said extensions.

In testimony whereof, I have hereunto subscribed my name this 28th day of November. 1922.

HARVEY CLAYTON RE} SCHLER. 

